WASHINGTON — As a child, Mitch McConnell contracted and largely beat polio. He was student president in high school, the University of Louisville and the University of Kentucky law school. He’s never lost a general election and has spent 30 years in the Senate scaling Republican leadership ranks.

Half a century after his first Washington stint as an intern, the methodical Kentucky Republican is now poised to achieve his long-cherished goal: becoming Senate majority leader.

McConnell was re-elected to a sixth term Tuesday as his party gained at least seven Senate seats — enough to control the chamber in next year’s Congress. McConnell, 72, is certain to be chosen by his GOP colleagues for the Senate’s most powerful job and will join House Speaker John Boehner, R-Ohio, in confronting Barack Obama with his presidency’s first Republican-controlled Congress.

“He’s right at the doorstep of the position he’s aspired to all his life,” said former Senate Majority Leader Trent Lott, R-Miss.

For McConnell, who’s been Senate minority leader for eight years, his ascension comes just in time. The 2016 election cycle looks tough for Republicans, who will defend 24 of 34 Senate seats.

Viewed by Democrats as excessively partisan but by both parties as a shrewd and tough tactician, McConnell has opposed Obama’s health care and financial regulation overhauls and environmental curbs that McConnell says damage his state’s coal industry.

He’s also shown a pragmatic side. He’s played pivotal roles in bipartisan accords that yielded a two-year extension of President George W. Bush’s tax cuts in 2010 and averted a 2011 federal default, the “fiscal cliff” across-the-board tax increases and budget cuts of 2013 and a federal shutdown that same year.

“Since he was 5 years old, he’s gotten up in the morning and all he thinks about is what he should do that day to acquire or maintain his political power,” said Rep. John Yarmuth, D-Ky., who’s known McConnell since 1968 in a mostly contentious relationship. “He’s the most focused individual I’ve ever known.”

Often monotone and stiff before TV cameras, McConnell is notably disciplined, rarely deviating — by even a word — from the written texts of Senate speeches and seldom engaging reporters in Capitol hallways. He attributes that focus to his mother, who he says administered physical therapy several times daily for two years after he got polio at age 2.

“This example of incredible discipline that she was teaching me during this period I always felt had an impact on the rest of my life,” he said in 2005.

After holding office locally, McConnell was narrowly elected to the Senate in 1984. He ousted Democrat Walter Huddleston after running TV ads starring a pack of hounds hunting for the incumbent, who McConnell said missed too many votes.

In the Senate, McConnell helped win federal buyouts for tobacco farmers and has been the GOP’s most relentless foe of efforts to limit campaign spending. He led the Senate GOP campaign organization for four years and became No. 2 Republican leader in 2003.

He’s been minority leader since 2007 — a period featuring intensified partisan clashes and growing numbers of GOP filibusters that each side blames on the other’s intransigence.

McConnell complains that Senate Majority Leader Harry Reid, D-Nev., has given Republicans little choice because he seldom lets them offer amendments to Democratic bills. Democrats accuse McConnell of snarling the Senate with over-the-top partisanship, citing his 2010 statement, “The single most important thing we want to achieve is for President Obama to be a one-term president.”

McConnell came to Washington in 1964 as a summer intern for Kentucky Sen. John Sherman Cooper, a liberal Republican. A year later, McConnell watched with Cooper as President Lyndon Johnson signed the 1965 Voting Rights Act.

McConnell has drifted further right over time, as have most Republicans, though many GOP senators are more conservative than he is.

“It’s inevitable if you’re going to be effective that you’ve got to adjust, especially as a leader of a caucus, that you’ve got to adjust to the tempo of the time,” said former Sen. Judd Gregg, R-N.H.

While McConnell has learned to work with his party’s most conservative members, the relationship has been unsteady.

He’s worked closely with his tea party-backed GOP colleague from Kentucky, Sen. Rand Paul — but only after Paul defeated McConnell’s establishment candidate in a 2010 primary. This year, McConnell had to fend off his own primary challenge from tea party conservatives.